In the Sunnyside Gardens area of the Special District, the floor area regulations of the underlying Residence and Commercial Districts shall not apply. In lieu thereof, the maximum floor area ratio permitted for residential, commercial and community facility uses, separately or in combination, shall be 0.75, which may be increased by up to 20 percent to a maximum floor area ratio of 0.9, provided that any such increase in floor area is located under a sloping roof which rises at least three and one half inches in vertical distance for each foot of horizontal distance, and the structural headroom of such floor area is between five and eight feet.